Temperature admittance spectroscopy of boron doped chemical vapor deposition diamond

Precision admittance spectroscopy measurements over wide temperature and frequency ranges were carried out for chemical vapor deposition epitaxial diamond samples doped with various concentrations of boron. It was found that the experimentally detected boron activation energy in the samples decreased from 314 meV down to 101 meV with an increase of B/C ratio from 600 to 18000 ppm in the gas reactants. For the heavily doped samples, a transition from thermally activated valence band conduction to hopping within the impurity band (with apparent activation energy 20 meV) was detected at temperatures 120–150 K. Numerical simulation was used to estimate the impurity DOS broadening. Accurate determination of continuously altering activation energy, which takes place during the transformation of conduction mechanisms, was proposed by numerical differentiation of the Arrhenius plot. With increase of boron doping level the gradual decreasing of capture cross section from 3 × 10⁻¹³ down to 2 × 10⁻¹⁷ cm² was noticed. Moreover, for the hopping conduction the capture cross section becomes 4 orders of magnitude less (∼2 × 10⁻²⁰ cm²). At T > T_room in doped samples the birth of the second conductance peak was observed. We attribute it to a defect, related to the boron doping of the material